Technical information

IM-P343-29 CH Issue 5 47
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9.6.3 S-MAX - valve shut-off maximum
Programming notes
Provides the facility to fully inflate the actuator at a pre-determined input signal.
The value set is a percentage of the input signal span range, i.e. setting a value
of 10% with an input span range of 4 - 20 mA (16 mA), will cause the valve
to close with an input signal of 18.4 mA i.e. 20 mA - 1.6 mA (10% of 16 mA).
Maximum setting is 20%.
Default values will depend on the selection of valve type (2-port or 3-port) and
control action (direct or reverse) as follows:
Valve type Direct Reverse
2-port Off 0.1%
3-port 0.1% 0.1%
For direct action (dIRCT) can only be set if MAX-T = 100% (will inflate the
actuator at set value). For reverse action (REV) can only be set if MIN-T = 0%
(will vent the actuator at set value).
Press and keys to alter displayed value. Press key to accept the
displayed value and advance to the characterisation (CHAR).
Commissioning notes
With an actual input signal of 20 mA and a maximum span range setting (MAX-R) of
20 mA may cause the valve plug to hover over the seat preventing tight closure with the
possibility of erosion damage to the plug and seat. Setting a shut-off value can help prevent
this by providing early closure of the valve.
9.6.4 CHAR - valve characterisation
Programming notes
Provides selection of linear (LIN), equal percentage (EQUAL) or fast opening
(FAST) characterisation. Characterisation is the relationship between input
signal and valve lift. Default value is Linear (LIN).
Use and keys to select the desired action. Press key to accept the
displayed characterisation and advance to time open (T-UP).
Commissioning notes
The standard characterisation for 2-port and 3-port valves is linear (LIN). For special
applications using 2-port valves an equal percentage (EQUAL) or fast opening (FAST)
characteristic can be selected. With equal percentage the valve will start to open slowly
and gradually accelerate opening related to input signal. With fast opening characteristic
the valve will commence to open quickly and gradually slow down opening related to
the input signal. This action is in addition to the valve trim flow characterisation (refer to
Figure 43 for guidance).
Fig. 43
Valve lift
Signal (mA)
Ratio 1:50
Ratio 50:1
Valve lift
Signal (mA)
Valve lift
Signal (mA)
Ratio 1:1